Plate heat exchangers are well known for producing a heat exchange between two fluids. They consist of a stack of plates clamped against each other in a sealed manner with a sealing joint being intercalated so as to create fluid flow channels between these plates, each plate comprising four holes forming with the holes of the other plates four manifolds, namely two inlet manifolds and two outlet manifolds, the ends of these manifolds being connected, on one side of the stack, to inlet or outlet pipework, so as to create two distinct fluid circuits, the joints enabling the channels to communicate with one or the other of the said fluid flow circuits.
Generally, the channels formed between the plates are, by virtue of the abovementioned joints, allocated to one or the other of the fluid circuits with a configuration alternating from one channel to the other. The inlet and outlet pipes are arranged along a diagonal of the plates which have a rectangular shape. In addition, the inlet pipework of a circuit is arranged on the same small side of the rectangle as the outlet pipework of the second circuit such that the two fluids flow in opposite directions. The opposite ends of the manifolds to the connection with the inlet or outlet pipework are closed off.
These heat exchangers are very efficient but they have the disadvantage of being choked by the impurities conveyed by the fluids. In particular, in the case of the auxiliary cooling circuits of a power station, the cooling fluid consists of untreated water which contains impurities.
When debris having dimensions which are greater than the distance separating two neighbouring plates, that is to say the thickness of the flow channel, are trapped in the inlet manifold and when there is a considerable quantity of these debris, the exchanger is choked and becomes unusable.
The problem of periodically unchoking the plate heat exchangers of the abovementioned type therefore arises.
A first solution consists in reversing the flow direction of the fluid in the choked circuit; this first method greatly complicates the layout of the pipework and requires the installation of three valves.
A second solution involves an at least partial dismantling in order to extract therefrom the debris which have become caught between the plates. This last solution results in a considerable labour cost and in a relatively long time during which the exchanger is unusable.
Another solution consists in installing a filter upstream of the inlet manifold. This solution is relatively costly and complex to install.